A fragment of the monkey f-receptor gene was cloned using reverse transcription reaction and polymerase chain reaction (PCR). The resulting 293 bp PCR product was subcloned into pGEM-TR (Promega), and used in ribonuclease protection assay and in situ hybridization. Monkey f-receptor cRNA probes were synthesized from the pGEM-TR recombinant using the MAXIscript in vitro Transcription Kit (Ambion, Austin, TX), purified with FullengtherTM (DWARF Science, Aloha, OR), and ethanol precipitated. Sense RNAs were transcribed by SP6 RNA polymerase, and the standard curve generated was used to quantify f-receptor mRNA levels in RNA samples obtained from discrete regions of the monkey brain. In order to illustrate the distribution of f-receptor mRNA in the fetal monkey brain, preliminary experiments have been performed on days 40, 45, 60 and 70 fetal brains. The f-receptor mRNA can be detected in the striatal area and the thalamus of day 40 fetal monkeys. By day 60 f-receptor mRNA can be detected in the striatum, olfactory bulbs, globus pallidus, thalamus and the medial habenula. These data indicate that the f-receptor mRNA is expressed early in gestation in the fetal monkey brain. Presently, we are elucidating the effects of gestational cocaine exposure on the development of f-receptor mRNA and receptor binding.